A typical procedure for the production of flexographic plates requires the preparing of a film which contains the image data required. The film is then attached on top of a photopolymer followed by exposure of the photopolymeric material to UV radiation through the film. One of the major drawbacks of this procedure is the deterioration of the quality of the image which is formed on top of the photopolymer due to UV light diffraction caused by the film base material.
Ink-jet technologies have been employed in the production of UV masks on top of photopolymeric materials, by direct printing of a desired image on top of the photopolymer, thereby eliminating the use of film. However, due to the limited viscosity of ink formulations applicable to ink-jet technologies, being typically 3-20 cPs, high print quality of the image cannot be achieved and problems such as bleeding, strike-through, clustering or feathering of the ink droplets have been observed.
Different strategies have been proposed as means to overcome problems associated with low printing quality, as for example is the case with ink-jet printing, among which is the use of an ‘ink-jet substrate’. According to this proposed ‘freezing by absorption’ strategy, a substrate having a thin absorptive layer on its surface is used to absorb the ink droplet, and to thereby minimize alternations in drop size and maintain high image quality.
A different approach to achieving high printing quality is the ‘freezing by chemical reaction’ approach in which a substrate having a thin layer of a reactant on its surface is allowed to chemically undergo a reaction with a second reactant which is present in the ink. Once the ink droplet comes into contact with the thin layer on the surface of the substrate, an instantaneous chemical reaction occurs, which results in the immobilization of the ink droplet on the surface of the substrate.
The major difference between the two approaches (‘freezing by absorption’ and ‘freezing by chemical reaction’) is the nature of the substrate coating. While ink absorption requires a thick enough layer to absorb the whole ink droplet, the chemical approach requires a very thin layer of the reactant to be introduced on top of the substrate (typically <3 μ of a dry layer). This layer may be introduced onto any substrate, either before or as part of the printing process itself.
The technology utilizing the ‘freezing’ approach was mainly used for printing on paper, vinyl substrates as well as on offset plates. U.S. Pat. No. 6,833,008 to Nitzan et al. discloses a method for printing applications using water-based ink. Applying such a method in flexographic printing resulted in a very large ink-drop diameter of 200 microns, though having sharp edges, as compared to printing without applying the method.
Regular ink jet printing requires standard optical densities which are easily achievable by using dyes or pigment dispersions in the ink. However, several applications require exceptional high optical densities, for example, medical images, transparent boards and UV masks for photopolymeric imaging. Medical images, such as radiographic images, are typically viewed on a blue transparent support and require a high optical density, i.e., usually higher than 3.00 OD. Medical images of such high optical density are typically obtained by means of silver technology, in which an image is formed by exposing a light-sensitive silver salt to light and the subsequent development of the resulting black silver (by reduction).
The progress and development of the ink-jet technology and the higher costs associated with the silver technology have increased the desirability and the demand for obtaining medical images with ink jet technologies. However, the ink-jet technologies are associated with a problem unique only thereto; when high-density printing is conducted on a transparent recording medium, relatively high maximum optical densities in the image are harder to achieve as compared with the relatively high optical density of images obtained with the silver salt method.
U.S. Pat. No. 5,621,448 to Leo et al. and U.S. Pat. No. 5,621,449 to Leenders et al. disclose recording methods combining silver salts and ink-jet technology. U.S. Pat. No. 6,440,896 to Szajewski et al. and U.S. Pat. No. 6,197,722 to Irving et al. disclose the use of a dye coupler to intensify the color of the image post printing. WO1999063406 discloses a silver based method of manufacturing a photomask. WO2001009679 discloses a silver based method for producing photomask utilizing a laser plotter.
U.S. Pat. No. 6,342,096 to Kurabayashi et al. discloses an ink-jet recording method comprising applying a plurality of inks to a recording medium by an ink-jet system to form dual- or multi-toned image on the recording medium.
U.S. Pat. No. 6,341,855 to Kurabayashi et al. discloses an ink jet recording method capable of providing a record that has highly transmissible image density.
U.S. Pat. No. 6,059,404 to Jaeger et al. discloses an ink jet printing method and apparatus for the production of a high quality images having varying color intensities.